Engine systems often include a starter motor configured to rotate a crankshaft of the engine prior to combustion of fuel and air within engine cylinders. The starter motor provides the engine with an initial source of torque in order to transition the engine from rest to an operational mode in which the engine combusts fuel and air to rotate the crankshaft. However, a starter motor may increase a cost and/or weight of the engine system.
Attempts to address reducing the cost and weight of the starter motor include reducing a size of the starter motor and/or a number of components included by the starter motor, and/or adjusting engine parameters to reduce starter motor load. One example approach is shown by Halimi et al. in U.S. Pat. No. 6,182,449. Therein, a two-cycle internal combustion engine is disclosed including a motor-assisted turbocharger that provides charge air for running the engine. The motor-assisted turbocharger may be arranged in series with an exhaust-driven turbocharger, and during startup, the motor-assisted turbocharger may provide charge air to the engine. When sufficient air pressure is available from a compressor of the motor-assisted turbocharger, the engine is cranked over by a starting motor.
However, the inventors herein have recognized potential issues with such systems. As one example, starting of the engine in such systems may be dependent on both of the motor-assisted turbocharger and the starting motor. During conditions in which the compressor of the motor-assisted turbocharger is unable to deliver sufficient air pressure, the starter motor may be unable to supply enough energy to start the engine. Similarly, during conditions in which the starter motor experiences degradation or power loss, the engine may be unable to start.
In one example, the issues described above may be addressed by a method for an engine, comprising: during an engine start request, driving a crankshaft of the engine without combustion only by flowing compressed air from an electric turbocharger to cylinders of the engine and without actuating a starter motor. In this way, the crankshaft may be rotated via only the compressed air prior to combustion of fuel and air in engine cylinders in order to start the engine.
As one example, the engine may include electrically or pneumatically actuated intake valves and exhaust valves, and the amount of opening of the intake valves and exhaust valves may be adjusted by a controller of the engine during engine startup. The controller may adjust the amount of opening of the intake valves and exhaust valves in order to decrease an amount of force delivered by the pressurized air to move pistons disposed within the engine cylinders and to rotate the crankshaft. In this way, the engine may be cranked without a starter motor, and a cost and weight of the engine may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.